Computer security experts investigating Internet attacks on Google and other U.S. companies say computers at Chinese educational institutions may have been involved, according to U.S. media reports.

The attacks may have started as early as April, unnamed sources involved in the investigation told The New York Times, according to a report on its Web site late Thursday. When Google revealed in January that its systems had been attacked, it put the start of the events no earlier than December.

Shanghai Jiaotong University and Lanxiang Vocational School are the two institutions said to be involved in the attacks, the New York Times said, citing several unnamed persons with knowledge of the investigation.

Investigators had previously tracked the attacks back to servers in Taiwan.

However, hackers often disguise their identity by sending commands through a number of computers on their way to a target. Even if further investigation backs up the findings cited in the latest news reports, that may not point to Chinese involvement in the attacks, as the real trail could go back further still. Investigators are still pursuing a number of theories, according to a report on Web site of The Wall Street Journal on Friday.

Google announced on Jan. 12 that attackers had tried to break into the Gmail accounts of Chinese human rights activists. In investigating the attacks, it said, it found other U.S. companies in the Internet, finance, technology, media and chemical sectors had also been attacked.